1. Field of the Invention
The present invention relates to annulus pressure responsive downhole tools. Particularly, the present invention provides a low pressure responsive tester valve.
2. Description of the Prior Art
It is well known in the art that downhole tools such as testing valves, circulating valves and samplers can be operated by varying the pressure of fluid in a well annulus and applying that pressure to a differential pressure piston within the tool.
The assignee of the present invention has recently developed an annulus pressure responsive tool which operates in response to a relatively low annulus pressure increase as shown in U.S. Pat. Nos. 4,422,506 and 4,429,748, both to Beck and assigned to the assignee of the present invention.
These low pressure responsive tools shown in U.S. Pat. Nos. 4,442,506 and 4,429,748 have a power piston which is exposed to well annulus pressure from above, and which has its lower surface exposed to pressurized nitrogen gas in a nitrogen chamber located therebelow. Located below the nitrogen chamber is a metering chamber or equalizing chamber which is filled with oil. A floating piston separates the gas in the gas chamber from the oil in the metering chamber. Disposed in the metering chamber is a metering cartridge which provides a resistance to flow of oil therethrough. The lower end of the metering chamber below the metering cartridge is communicated with well annulus pressure, and a second floating piston separates the oil in the metering chamber from well fluid which enters the lower end of the metering chamber. An increase in well annulus pressure is immediately communicated to the upper surface of the power piston, but is delayed for a significant period of time in being fully communicated to the lower side of the power piston, so that a rapid increase in well annulus pressure will cause a downward pressure differential across the power piston to move the power piston and actuate the tool.
A number of modifications of the basic low pressure responsive tool have been developed by the assignee of the present invention as illustrated in U.S. Pat. No. 4,537,258 to Beck.
One particular feature of such tools to which many of the alternative designs developed by the assignee of the present invention have been directed is the provision of a means for controlling the position of the tester valve during changes in well annulus pressure. That is, while the normal operation of the tool provides for opening and closing of the ball valve in response to reciprocating motion of the power piston, it is sometimes desired to be able to maintain the ball valve in either a closed or an open position during changes in well annulus pressure.
One particular situation addressed by the present invention is the need to leave the tester valve open without maintaining an increased annulus pressure. This is useful when spotting fluids such as acid or cement down to the level of the subsurface formation, or when displacing fluids from the test string with nitrogen gas.
Numerous approaches have been utilized to control the movement of the valve.
Often, an actuating mandrel associated with the valve is initially shear pinned in place to hold the valve closed while running into a well, as shown for example in FIG. 2b of U.S. Pat. No. 4,422,506.
U.S. Pat. No. 4,429,748 to Beck discloses in FIG. 2c thereof a resilient ring assembly 206 to positively control the full opening and closing of the ball valve such that the ball valve is prevented from only partially opening or closing. The Beck U.S. Pat. No. 4,429,748 does not provide a means for leaving the ball valve in an open position when well annulus pressure is reduced to hydrostatic pressure. It includes a return spring 408 which will reclose the ball valve regardless of how slowly well annulus pressure is reduced.
U.S. Pat. No. 4,537,258 to Beck discloses several embodiments of such tools. The embodiment disclosed in FIGS. 2A-2E and FIG. 3 thereof utilizes a lug and slot arrangement disposed between the power piston and the housing for controlling movement of the power piston relative to the housing.
The embodiment disclosed in FIGS. 5A-5G of the Beck U.S. Pat. No. 4,537,258 uses a spring-loaded pin and detent arrangement 600 for locking the actuating mandrel in a position corresponding to an open position of the ball valve. Again, the spring-loaded detent arrangement 600 cannot hold the ball valve of the Beck U.S. Pat. No. 4,537,258 in an open position when well annulus pressure is reduced to hydrostatic pressure. As pointed out at column 23, lines 60-62, the coil spring 656 will overcome the releasable holding means 600 to reclose the ball valve, regardless of how slowly well annulus pressure is reduced to hydrostatic pressure.
U.S. Pat. No. 4,355,685 to Beck and assigned to the assignee of the present invention shows a circulating valve having an annulus pressure responsive operating means similar to that of the tools just discussed, and including a lug and slot arrangement disposed between the power piston and the housing as seen in FIG. 1C and FIG. 4 thereof for controlling the position of the power piston relative to the housing. The lug and slot arrangement of the Beck U.S. Pat. No. 4,537,258 includes a spring biased ball 124 seen in FIGS. 1C, 5 and 6, which is structurally somewhat similar to the spring-loaded ball 426 seen in FIG. 2C and FIGS. 3, 4 and 5 of the present application, although the ball 124 of the Beck U.S. Pat. No. 4,537,258 serves a completely different purpose than does the ball shown in the present invention.
Another device recently developed by the assignee of the present invention is a multi-mode testing tool shown in U.S. patent application Ser. No. 596,321, filed Apr. 3, 1984, of Ringgenberg. It is noted that application Ser. No. 596,321 itself is not prior art to the present invention; that application is being referred to only as a convenient means for describing one embodiment of the tool shown therein which is a part of the prior art. Application Ser. No. 596,321 shows several embodiments of a ratchet means for operably connecting an actuating mandrel to a power piston to control the opening and closing of the valve in response to changes in well annulus pressure, but only the embodiment shown in FIG. 10 thereof is a part of the prior art.
One prior art apparatus which can have its valve means left in an open position in response to a relatively slow bleed-off of well annulus pressure is that disclosed in FIGS. 5C and 5D of U.S. Pat. No. 4,448,254 to Barrington, and assigned to the assignee of the present invention. The Barrington device operates based upon compression of silicone oil, rather than compression of an inert gas. The embodiment shown in FIGS. 5C and 5D of Barrington does not include a releasable retaining means for retaining the power piston in a position corresponding to an open position of the valve, as pointed out at column 13, lines 17-19 of that patent. Utilizing the device of FIGS. 5C and 5D of the Barrington U.S. Pat. No. 4,448,254, it is possible to leave the ball valve in its open position if well annulus pressure is slowly reduced to hydrostatic pressure.
The Barrington device was provided with a fluid restriction having a larger flow path in the depressurizing passage than was provided in the pressurizing passage of its metering cartridge, so that a shorter time delay was provided for well annulus pressure decreases than for well annulus pressure increases. The time delay provided for well annulus pressure decreases was approximately two-thirds that provided for comparable well annulus pressure increases.
The Barrington U.S. Pat. No. 4,448,254 included both a main power piston 400 and a booster piston 402 as seen in FIGS. 5C and 5D and described at columns 13-15 of that patent. The booster piston 402 aided in the ability of that tool to be left in an open position, because if well annulus pressure was bled off somewhat faster than could be relieved by the fluid restrictor of the depressurizing passage, the booster piston 402 could move upwards to accommodate the upward differential pressure surge without moving the power mandrel upwards and reclosing the ball valve.